The present invention relates to a disc brake, in particular for commercial vehicles.
There are closed-loop brake control systems for disc brakes, with which systems the wheel rotational angle and the wheel speed are measured by means of electrical signal pulses. Here, a so-called magnet wheel, which has magnetic properties which alternate at predefined angular intervals, is usually attached to a part of the vehicle wheel. A sensor, which is fixed relative to the axle, is arranged at the magnet wheel which rotates when the vehicle is moving. The arrangement is such that the alternation of the magnetic states of the magnet wheel induces electrical pulses in the sensor as it moves past the sensor, which electrical pulses can be evaluated and are transmitted to an evaluating electronic unit via a line connection.
Previously known closed-loop brake control systems have the disadvantage that the sensors are frequently liable to faults on account of the environmental conditions. Since the brake rotor of the wheel brake is inevitably also connected to the wheel hub, there is high thermal loading at the installation position of the sensor, which thermal loading can lead to melting of the plastic housing of the sensors and to charring of the cables which carry the signal. The sensitive inner components of the sensors are damaged as a result of this exposure to a high heat, and this can ultimately result in a functional failure. For increased safety, particularly heat-resistant materials must therefore be used in a complex way.
German patent document DE 44 02 959 presents a disc brake having a device for pulse generation at vehicle wheels, in which a magnet ring is arranged on a brake disc. A sensor, by which the wheel speed can be measured, is provided adjacent to the magnet ring. As a result of being arranged directly adjacent to the brake disc, the sensor is subjected to increased loading.
In addition, in German patent document DE 102 07 011 A1, a sensor for measuring rotational speed is provided on an axle of a motor vehicle, in which the sensor is fastened in an axially running opening in the stub axle. As a result, the sensor can be arranged in a largely protected manner, the assembly and production being comparatively complex.
There is therefore needed a disc brake, in particular for commercial vehicles, which makes reliable measurement of the rotational speed and of the rotational angle possible, and during which process the operation of the sensor should not be affected by environmental influences.
This need is not by a disc brake, in particular for commercial vehicles having a brake caliper which straddles a brake disc; a pneumatically or electromotively actuable brake application device, arranged in the brake caliper, for applying the brake; a magnet wheel, which rotates with the brake disc; and a positionally fixed sensor for measuring the rotational angle and the rotational speed of the magnet wheel, wherein the sensor is arranged at a distance from the magnet wheel, and at least one line for transmitting pulses is connected between the sensor and the magnet wheel.
According to an aspect of the invention, the sensor for measuring the rotational angle and the rotational speed of the magnet wheel is arranged at a distance from the magnet wheel, and at least one line for transmitting pulses is connected between the sensor and the magnet wheel. As a result, the installation position of the sensor, which is sensitive to environmental influences, may be arranged at a distance from the magnet wheel, so that the thermal loadings which occur at the magnet wheel as a result of the brakes being applied no longer occur at the sensor. The sensor can, in fact, also be arranged in a protected region, it being possible for the rotational speed and the rotational angle to be measured in a manner known per se, since at least one line for bridging the distance to the sensor is connected between the magnet wheel and the sensor.
According to a preferred embodiment, the line for transmitting pulses includes a soft iron rod. As a result, the pulses generated by magnets may be transmitted-on in a simple manner. The one or more soft iron rods are relatively insusceptible with regard to the temperature differences which occur. Alternatively, a corresponding optical light guide may be used for transmitting pulses or light signals in an optical measuring system.
For particularly good protection of the line and of the sensor for measuring the rotational angle and the rotational speed, a separating wall is preferably arranged between the line and the magnet wheel. This also avoids dirt adversely affecting the measurement by means of the line and the sensor. The separating wall is preferably formed by a non-magnetic metal separating plate, which does not impede the measurement of the signals and additionally constitutes a good thermal conductor, so that when thermal loading occurs, it can be quickly dissipated again over a large area.
For simple assembly of the measuring unit, the sensor is mounted on a printed circuit board, which may be accessed by removing a cover. As a result, the printed circuit board and the sensor can, if necessary, be easily exchanged in the event of a functional failure. For easy accessibility, the sensor may be mounted adjacent to the brake application device, on that side of the brake caliper which faces away from the brake disc.
For a simple construction of the measuring unit, the sensor is formed from a Hall sensor and a permanent magnet, which is then connected to a corresponding electronic circuit. The disc brake according to the invention is particularly suitable for exemplary embodiments in which an electronic circuit is provided for the open-loop and closed-loop control of the readjustment due to brake lining wear. This is because the many electrical components can be mounted on one common printed circuit board. Here, it is possible to use the present electronic circuit to evaluate the sensor signals, and to use a data bus (for example, a CAN bus) to make the information available to the electronic circuits connected downstream, if such a data bus is present.
Both active and passive sensors may be used for measurement, the active sensors being connected to an electrical voltage source. In the case of active sensors, the magnetic circuit can be split between two lines, which each separately connect the magnetic circuit between the magnet wheel and the sensor.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.